The problem of providing power inductively to moving vehicles along a roadway has been discussed for many years, to overcome the range anxiety associated with pure electric vehicles (EVs) i.e. electric vehicles which rely solely on electric energy. The ability to provide power continuously, or at least sufficiently often, while the vehicle is travelling has many benefits. These include: minimisation of on-board energy storage and vehicle weight; and elimination of the long charging times required when available power sources are dispersed and only used when an EV's power supply is low.
Charging or powering electric vehicles inductively from a roadway has been proposed previously in paper publications. The solutions proposed for providing a roadway powered electric vehicle (RPEV) system discuss means by which small sections of roadway include embedded inductive loops which may be energised when a vehicle requiring charge is determined to be in the proximity. This eliminates the need to power large sections of highway and increases the efficiency of the system. In all cases a number of inductive loops are spaced along a highway but they are directly connected to a power supply typically operating at frequencies between 1-10 kHz. Each inductive loop is selectively energised by direct switching means when a vehicle is detected to be in the proximity. Inductive receivers on-board the vehicle are elongated in the direction of the highway and normally controlled to be in close proximity with the roadway when the vehicle is moving.
For example, U.S. Pat. Nos. 4,331,225 and 4,836,344 describe means by which an electrochemical battery may be charged as a vehicle travels along an inductive highway. In U.S. Pat. No. 4,836,344 controllable relays are used to switch on and off sections of highway transmitter modules of around 3 m in length to deliver power to a vehicle as it moves along the roadway surface. The inductive roadway modules are elongate, being oriented longitudinally in the direction of the roadway, and placed end to end along the centre of the roadway. Power control to the vehicle is enacted from the roadway side simply by temporarily switching off the roadway power modules as required. U.S. Pat. No. 4,331,225 by the same author describes means by which the desired vehicle receiver is lowered to ensure the air-gap between the vehicle pick-up receiver and the roadway inductive track is as small as possible during operation, while capacitor switching means is also employed to modify the pick-up tuning to compensate (and thereby regulate the output voltage of the compensated receiving coil) for any reluctance variations during driving.
In U.S. Pat. No. 5,207,304, Lechner describes improvements to the magnetic structure of both the roadway transmitter coils and the receiver on board the vehicle. U and W shaped magnetic cores are suggested. Variable switchable compensation capacitors are described to enable power control and regulation to a battery
In U.S. Pat. No. 5,311,973, Tseng describes the addition of radio communications to control the switching of the primary coils and sensors to help guide the vehicle along the inductive loops. Further information relating to means by which specific vehicle recognition and billing is also described.
U.S. Pat. No. 5,821,728 describes a system that combines many of the above elements from earlier patent publications. Again the system requires the pick-up receiver on the vehicle to be lowered to take power from a roadway with inductive coupling strips along the centreline of the road.
In U.S. Pat. No. 6,879,889 a fast charging system is proposed that relies on a rapid charge energy storage device such as an electromechanical battery (EMB). As a result clusters of inductive transmitter modules (each with a single elongated flat pancake coil of roughly 3 m by 65 cm) placed longitudinally along the roadway centre are proposed that only need to be installed in less than 10% of the highway. To be effective these power transmitters require relatively high charging rates (a minimum power transfer of 100 kW-140 kW delivered continuously to an EV while it is in motion above the transmitter modules). In order to improve coupling between the roadway transmitter modules and the receiver coils while the EV is in motion along the highway an adjustable ride-height suspension and alignment is suggested. For garaging and/or stops along the roadside/at lights or other convenient places, the high charging rates require the pick-up to be lowered to near zero air-gap. Parking is assumed to be within 100 mm laterally but a mechanism for adjusting the receiving coil to within 10-20 mm in the lateral direction is proposed. Under such stationary charging there are suggested means for heating the road to ensure a build up of snow or ice does not stop the pick-up lowering mechanism from operating correctly. The scheme requires heating elements embedded in the road which each can take as much as 10% of the delivered power. Communications means for data and billing are also described.